There could be any number of reasons for dogs licking floors/carpet, walls and even bedspreads or cushions. When a dog is stressed or bored, obsessive-compulsive behaviors may develop. Distractions, providing interest and outlets, attention directed elsewhere on a consistent basis may resolve the problem, but it takes dedication and perhaps even a slight lifestyle change on the part of the humans.
In an older dog like yours, Hypoadrenocorticism (Cushing's Disease), liver failure or neurological disease may also be at least part of the cause.
It may be a tooth or gum problem too.
Assessment by a veterinarian is necessary in order to rule out physical cause.
Other abnormal ingestive behaviors include Pica (eating non-food items), Coprophagia (ingesting feces on purpose), Polyphagia/aerophagia/psychogenic water drinking beyond necessary or healthy amounts to maintain daily fluid balance.
There may be a cognitive dysfunction (senility/dementia) or simply attention-seeking. When there's cognitive changes they also typically include confusion, not seeming to remember commands/tricks or where they are in the house. They may soil inside the house, on beds/furniture and become disoriented easily. Changes in sleep pattern are also noticed, with pacing and barking.
Currently there is only one approved medication (Selegiline) for canine cognitive dysfunction. It must be administered for life and regular renal evaluations are necessary to be sure there's no hepatic side effects (liver disease/failure).
When physical causes of compulsive licking is ruled out (and it must be ruled out first), addressing the OCD (Obsessive Compulsive Disorder) with behavior modifications and consideration of medication may be undertaken.
This could be the result of fear, anxiety, hyperactivity, boredom, stress or any combination.
Find out more here: http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/140217.htm&hide=1
Please let me know how this goes with him ok?